Escitalopram is the eutomer (i.e., the enantiomer of a chiral compound that is more effective for a particular action) of the racemic drug citalopram. Specifically, it consists of the S-enantiomer. Escitalopram has the highest affinity to the human serotonin transporterSERT and different from other SSRI binds to both, the primary and the allosteric binding site of the SERT.[2]. The allosteric binding has a self-potentiating effect of the binding to the primary binding site, leading to a more effecte serotonin-reuptake inhibition. However the increased activity has been argued by some experts to be statistically and clinically insignificant.

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Escitalopram oxalate is derived from the drug citalopram which is a mixture of two mirror-image isomers, only one of which (S-citalopram) is thought to be responsible for the antidepressive effect of the medication, while the other (R-citalopram) has been shown to counteract the antidepressive effect. Lundbeck has split the isomers apart, taken the active isomer and has licensed it as the new drug Escitalopram. Escitalopram is the pure S-enantiomer (left-handed isomer) of the racemicbicyclic phthalane derivativecitalopram, and is the most selective SSRI[3].

Escitalopram was released two years before the patent for citalopram was due to expire. The expiration of a patent means other companies can legally produce cheaper generic versions. On May 23, 2006, the FDA approved a generic version of escitalopram by Teva[2]. However, on July 14th, 2006 the the US District Court of Delaware decided in favour of Lundbeck regarding a patent infringement dispute and ruled the patent on escitalopram valid.[3]

The recommended dosage of Lexapro is 10-20 mg a day. Exceptions include the elderly, who should only take up to 10 mg a day, and pregnant women in their third trimester should not use Lexapro at all.[4] As both Generalized Anxiety Disorder (GAD) and Depression are both considered chronic conditions, treatment is recommended for several months. However, the efficacy of Lexapro over long periods of time has not been studied, therefore consistent reevaluation of the treatment is recommended for longer periods of treatment.[4]

The side effect profile of escitalopram is close to that of other SSRI with nausea, somnolence and gastronintestinal side effects, leading. SSRIs have been shown to cause sexual side effects in most patients, both males and females[5]. Although usually reversible, these sexual side effects can sometimes last after discontinuation. This disorder is known as Post SSRI Sexual Dysfunction. It may also cause weight gain in certain people. It may cause dizziness after exercise in children.

Discontinuation from antidepressants, especially abruptly, has been known to cause certain withdrawalsymptoms. One possible discontinuation symptom from Escitalopram is a type of spontaneous nerve pulse known as paresthesia or "electric shock sensations", described by some patients as a feeling of small electric shocks, which may be accompanied by dizziness. These pulses may be short in duration, only milliseconds long, may affect any region of the body, and recur up to several times a minute, throughout all waking hours. They can be increased by physical activity, but are not solely linked to muscular activity. Other discontinuation symptoms include extreme sensitivity to loud sounds and bright lights, chills, hot flushes, cold sweats, reddening of the face, abdominal pain, weight gain and extreme mental fatigue. Also possible is severe irritability and sadness/depression like symptoms.[6]